Phase 2 : dérive, ImpactScore, slider temporel

Backend :
- OpenMeteoClient : vent horaire 72h (gratuit, sans clé)
- DriftSimulationService : échantillonnage ST_GeneratePoints,
  déplacement itératif Stokes 3%, reconstruction ST_ConcaveHull,
  4 horizons H+6/12/24/48, confiance décroissante
- ImpactScoreService : score 4 composantes (distance/densité/
  vitesse/tendance), cache Redis TTL 3h, invalidation à chaque calcul
- ComputeForecastsCommand : traite les observations sans forecast
- SpotScoreController : score courant + horizons depuis forecasts

Frontend :
- TimelineSlider : navigation Now/+6h/+12h/+24h/+48h
- SargassesMap : couche observations (orange) vs forecasts (violet)
  rechargée à chaque changement d'étape
- SpotPanel : affichage score par horizon actif + indicateur confiance
- Build → backend/public/spa/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/Command/ComputeForecastsCommand.php

@@ -0,0 +1,89 @@
+<?php
+
+namespace App\Command;
+
+use App\Entity\SargassumObservation;
+use App\Service\Forecast\DriftSimulationService;
+use App\Service\Forecast\ImpactScoreService;
+use Doctrine\ORM\EntityManagerInterface;
+use Symfony\Component\Console\Attribute\AsCommand;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
+
+#[AsCommand(
+    name: 'app:compute-forecasts',
+    description: 'Calcule les forecasts de dérive et les ImpactScores pour les dernières observations',
+)]
+class ComputeForecastsCommand extends Command
+{
+    public function __construct(
+        private DriftSimulationService $drift,
+        private ImpactScoreService     $scores,
+        private EntityManagerInterface $em,
+    ) {
+        parent::__construct();
+    }
+
+    protected function configure(): void
+    {
+        $this->addOption('limit', 'l', InputOption::VALUE_OPTIONAL,
+            'Nombre max d\'observations à traiter', 5);
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        $io    = new SymfonyStyle($input, $output);
+        $limit = (int) $input->getOption('limit');
+
+        $io->title('Calcul forecasts + ImpactScores');
+
+        // Observations récentes sans forecast
+        $observations = $this->em->getRepository(SargassumObservation::class)
+            ->createQueryBuilder('o')
+            ->leftJoin('o.forecasts', 'f')
+            ->where('f.id IS NULL')
+            ->orderBy('o.detectedAt', 'DESC')
+            ->setMaxResults($limit)
+            ->getQuery()
+            ->getResult();
+
+        if (empty($observations)) {
+            $io->info('Aucune observation sans forecast trouvée.');
+            return Command::SUCCESS;
+        }
+
+        $io->progressStart(count($observations));
+        $errors = 0;
+
+        foreach ($observations as $observation) {
+            try {
+                $forecasts = $this->drift->computeForecasts($observation);
+                $io->text(sprintf(
+                    'Observation %s → %d forecast(s)',
+                    $observation->getId(),
+                    count($forecasts)
+                ));
+
+                $this->scores->computeForObservation($observation, $forecasts);
+            } catch (\Throwable $e) {
+                $io->error('Erreur sur ' . $observation->getId() . ' : ' . $e->getMessage());
+                $errors++;
+            }
+
+            $io->progressAdvance();
+        }
+
+        $io->progressFinish();
+
+        $io->success(sprintf(
+            '%d observation(s) traitée(s), %d erreur(s).',
+            count($observations) - $errors,
+            $errors
+        ));
+
+        return $errors === 0 ? Command::SUCCESS : Command::FAILURE;
+    }
+}